QE 
86 
T798W8 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


of  the  Region  of 
Tucson,  flrizona 

By  LAMBERT  WOOD 


METROPOLITAN  PRESS     .     .     PORTLAND,  OREGON 


FOREWORD 

7V;f  following  outline  of  Lambert  Wood's 
u~ar  ivork  appears  in  the  history  called  "Wil- 
liams College  in  the  World's  War,"  published 
by  the  president  and  trustees  of  Williams  Col- 
lege : 

FIRST  LIEUTENANT  LAMBERT  ALEXANDER  WOOD, 
commanding  the  Machine  Gun  Company,  9th  In- 
fantry, Second  Division,  was  killed  in  action  south- 
east of  Soissons,  in  France,  July  18,  1918. 

He  attended  the  training  camp  at  Plattsburg, 
N.  Y.,  in  the  summer  of  1916,  becoming  a  ser- 
geant, and  in  May,  1917,  received  a  reserve  com- 
mission as  Second  Lieutenant.  At  the  close  of  the 
first  O.  T.  C.  at  Plattsburg,  in  August,  1917,  he 
was  commissioned  First  Lieut.  U.  S.  A.,  and  was 
assigned  to  the  Machine  Gun  Company,  9th  Inf. 
Regulars,  then  stationed  at  Syracuse,  N.  Y.  His 
regiment  went  overseas  in  September,  1917,  and, 
as  a  part  of  the  Second  Division,  was  brigaded 
with  the  French,  going  up  to  the  front  in  March, 
1918,  and  participating  in  the  engagements  near 
Chateau-Thierry  and  the  recapture  of  Vaux,  in 


922289 


June  and  July,  which  blocked  the  German  third 
offensive.  On  June  6,  while  his  company  was  ad- 
vancing, it  was  subjected  to  a  German  barrage,  and 
also,  through  an  error,  the  American  artillery 
started  firing  on  the  same  position.  After  four  run- 
ners had  failed  to  reach  Base  Headquarters,  Lieu- 
tenant Wood  volunteered  and  succeeded  in  getting 
through,  stopping  the  fire  and  saving  many  lives. 
When  relieved,  early  in  July,  Lieutenant  Wood 
had  been  in  the  front-line  trenches  thirty-eight 
consecutive  days.  In  the  Aisne-Marne  offensive, 
during  the  advance  near  Soissons,  on  July  1  8,  he 
was  killed  in  action  while  directing  his  company, 
which  for  the  two  months  he  had  commanded  in 
the  absence  of  the  Captain. 

He  was  awarded  the  Distinguished  Service 
Cross  (Posthumously)  on  June  7,  1919,  with  the 
following  citation: 

"For  extraordinary  heroism  in  action  at  Cha- 
teau-Thierry, France,  June  6-7,  1918.  With  en- 
tire disregard  for  personal  danger,  Lieutenant 
Wood  passed  through  heavy  artillery  fire,  with 
a  message  to  stop  misdirected  supporting  artil- 
lery fire,  which  fire  imperiled  the  safety  of  his 
organization.  He  was  killed  near  Soissons, 
France,  on  July  18,  1918,  while  leading  his 


machine-gun  platoon  on  a  flank  movement 
against  an  enemy  group,  which  was  infilading 
our  advancing  infantry  line." 

— General  Orders,  No.  126,  War  Department, 
November  11,  1919. 

He  was  cited  in  General  Orders  No.  40,  Head- 
quarters Second  Division,  July  5,  1918,  and  in 
General  Orders  No.  53,  Headquarters  Second  Di- 
vision, September  12,  1918,  and  awarded  an  en- 
graved Citation  Certificate  by  the  Commanding 
General,  American  Expeditionary  Forces,  but  both 
citations  and  the  gallantry  certificates  were  can- 
celled because  of  the  higher  award  of  the  Distin- 
guished Service  Cross  for  the  same  acts. 

On  March  12,  1919,  Lieutenant  Wood  was 
posthumously  awarded  the  Croix  de  Guerre  with 
Gold  Star,  under  Order  No.  14,307  "D"  General 
Headquarters,  French  Armies  of  the  East,  with 
the  following  citation: 

"A  fait  preuve  d'une  grande  bravoure  dans  le 
commandement  de  sa  compagnie  de  mitrail 
lenses,  couvrant  le  flanc  gauche  tres  expose  de 
son  Regiment.  A  ete  tue  au  cours  du  combat,  le 
18  Juillet  1918,  au  Sud-Ouest  de  Soissons." 
("Gave  proof  of  great  bravery  in  the  command 


of  his  machine  gun  company,  covering  the  very  ex- 
posed left  flank  of  his  regiment.  Was  killed  in  the 
course  of  the  combat  the  18th  day  of  July,  1918, 
southwest  of  Soissons.") 


A  TRIBUTE  TO   LIEUTENANT   LAMBERT  WOOD 
BY  AN  ASSOCIATE  OFFICER 

A  GREAT  FRIENDSHIP  existed  between  Lieutenant 
Lambert  Wood  and  myself  while  in  the  service.  I 
can  say  that  he  was  just  in  his  decisions  with  the 
enlisted  personnel  of  his  command. 

He  always  demanded  that  the  men  meet  him 
half  way,  and  in  that  way  he  won  the  undying  re- 
spect of  all  the  officers  and  enlisted  men  in  the 
Battalion.  He  was  always  courteous  and  even-tem- 
pered. He  was  a  man  who  feared  nothing}  even  in 
his  last  moments  of  his  life.  He  wanted  to  know 
if  his  command  was  safe.  He  did  not  hesitate  even 
in  going  out  to  places  where  he  would  send  an  en- 
listed man,  and  in  doing  so,  he  won  the  everlasting 
respect  from  the  Battalion  personnel,  which  he 
carried  to  his  grave. 

I  frequently  wish  I  could  always  associate  in 
civil  life  with  men  as  calm  and  cool  as  he  was  un- 
der shell-fire. 

Yours  very  sincerely, 

Louis  H.  STRICKLAND, 
Sergeant  Co.  D.,  9th  Infantry. 
Second  Division. 


WILLIAMS  COLLEGE 
DEPARTMENT  OF  GEOLOGY  Williamstown.  Mass. 

December  13,  1918. 
MY  DEAR  MRS.  WOOD: 

I  am  sending  you  today  an  essay  which  your  son, 
Lambert,  wrote  while  taking  a  course  in  Geology 
with  me. 

There  have  been  few  students  in  Williams  Col- 
lege for  whom  I  have  such  a  strong,  personal  feel- 
ing as  I  had  for  your  son.  Although  he  was  a 
student  of  mine  for  less  than  a  year,  nevertheless, 
he  stood  out  from  among  his  class  mates  in  some 
indefinable  way.  It  may  have  been  his  manliness, 
or  his  kindliness  and  modesty,  or  all  combined. 
Whatever  it  was,  it  was  a  trait  we  all  admired. 

It  is  difficult  to  reconcile  the  loss  of  such  a 
manly  man  with  the  goodness  of  God,  but  I  have 
not  the  slightest  doubt  that  sometime  we  will  learn 
that  the  sacrifice  was  necessary.  There  was  a 
mighty  task  to  be  performed  and  he  was  one  who 
gave  his  life  for  its  accomplishment. 

The  letter  to  you  published  in  "Ephriam  Wil- 
liams: A  Soldier,"  was  just  like  him. 

I  do  not  wish  to  intrude  on  your  sorrow  or  to 
make  it  more  acute  by  sending  this  essay,  and  I 
hope  I  have  not  done  so.  With  deep  sympathy, 
I  am,  Sincerely  yours, 

— HERDMAN  F.  CLELAND. 


A  Geological  Sketch  of  the  Region 
of  Tucson,  Arizona 

By  LAMBERT  WOOD 

THE  VALLEY  of  Tucson  in  Pima  County,  Arizona, 
is  an  expanded  portion  of  the  valley  of  the  Santa 
Cruz  river.  At  Tucson,  the  river  occupies  the  west- 
ern side  of  the  valley  at  the  eastern  base  of  the 
Tucson  Mountains,  and  flows  northward  toward 
the  Gila  River,  but  sinks  in  the  sand  before  reach- 
ing it.  In  dry  seasons,  it  is  a  small  and  insignificant 
stream,  but  is  subject  to  great  floods  in  the  rainy 
seasons.  The  City  of  Tucson  is  situated  on  the  right 
bank  of  the  river. 

The  broad  valley  of  Tucson  has  the  appearance 
of  being  surrounded  by  mountain  ranges  on  all 
sides.  The  view  to  the  north  and  northeast,  is 
bound  by  the  high  and  rugged  range  of  the  Cata- 
lina  Mountains,  and  their  continuation  southward 


called  the  Rincons;  on  the  east  and  south,  by  the 
Whetstones  and  the  Santa  Ritas;  on  the  south- 
west, by  the  Sierritas,  and  west  by  the  Tucson 
Mountains.  The  Tortillitas  Mountains,  a  group 
lying  east  of  the  Catalinas,  form  a  part  of  the 
northern  and  western  boundaries  of  the  valley. 
The  region  so  enclosed  by  mountains  has  a  width 
of  from  eighteen  to  thirty  miles,  a  length  of  forty 
miles,  and  an  area  of  about  one  thousand  square 
miles.  The  altitude  is  from  twenty-four  hundred 
feet  at  Tucson,  to  thirty-five  hundred  feet  at  the 
foot  of  the  slopes  of  the  higher  ridges.  From  this 
margin,  the  ground  descends  toward  the  Santa 
Cruz  river,  and  in  the  middle  and  lower  portions, 
constitutes  what  is  known  as  the  "Mesa,"  appar- 
ently a  flat  plain,  but  in  reality,  a  continuous  slope, 
modified  locally  by  erosion.  There  is  a  great  va- 
riety in  the  age  and  composition  of  the  rocky 
ridges,  which,  rising  to  an  altitude  of  five  thousand 
feet  above  the  Mesa,  give  a  wide  range  of  climatic 
conditions  and  of  vegetation. 

The  principal  streams,  in  addition  to  the  Santa 
Cruz,  are  the  Rillito,  at  the  foot  of  the  Catalinas, 
north  of  Tucson;  the  Pantano  Wash,  rising  in  the 
Whetstones,  and  an  underground  flow  of  David- 
son's Canyon. 

The  chief  canyons  of  the  south   slope  of  the 


10 


Catalinas  are  the  Pima,  Pantano,  Sabino,  and  the 
Agua  Caliente. 

SANTA    CATALINA   RANGE 

It  presents  a  bold  rocky  front  toward  Tucson, 
and  rises  to  an  altitude  of  9,225  feet  in  Mt.  Lem- 
mon. 

The  central  nucleus  of  this  range  consists  of 
crystalline  rocks,  chiefly  granitic  and  gneissic. 

The  formations  on  the  southern  side  of  the  Cat- 
alinas, toward  Tucson,  are,  for  the  most  part,  pre- 
Cambrian  gneiss  and  mica-schists  in  tabular  form, 
regularly  stratified  and  with  included  sericitic 
schists,  all  believed  to  represent  some  of  the  oldest 
rocks  known,  equivalent  to  the  ancient  Huronian, 
Kewcenawan,  and  Laurentian  formation  of  Canada. 

The  pre-Cambrian  gneissic  rocks  are  also  largely 
developed  on  the  northeastern  flanks  of  the  Cata- 
linas, and  are  there  associated  with  highly  laminat- 
ed mica-schists,  the  Arizonian.  These  schists  are 
characterized  by  extreme  foliation  and  sharp,  angu- 
lar plication  presenting  zig-zag  lines  upon  exposed 
surfaces. 

Here,  also,  we  find  Paleizoic  strata  resting  un- 
conformably  upon  crystalline  schists  of  the  pre- 
Cambrian,  or  upon  a  broad  area  of  coarse  granite 
as  at  Oracle  or  in  the  Canyada  del  Oro. 


1  1 


The  foundation  granites  are  penetrated  by  great 
dikes  of  diorite,  which  have  changed  the  blue-grey 
limestones  to  crystalline  white  marble  as  at  Marble 
Butte.  Copper  ores  are  developed  along  the  con- 
tact, notably  at  Apache  Springs  and  Leatherwood's 
Camp. 

DEVONIAN   ROCKS 

Between  the  Southern  Belle  Canyon  and  Pepper 
Sauce  Gulch  a  long  ridge  extending  eastward, 
called  Coral  Ridge,  is  made  up  of  quartzite,  lime- 
stone and  shaly  limestones,  in  which  there  is  a 
bed  of  corals  and  shells  of  the  Devonian  age.  The 
fossils  are  of  especial  interest  because  of  their  won- 
derful preservation  in  every  detail  of  structure. 
This  is  due  to  the  permiation  of  the  rock  by  sili- 
cious  waters,  which  have  changed  the  organized 
structure  from  carbonate  of  lime  to  silica,  and  have 
left  the  surrounding  limestone  unchanged.  The 
weathering  of  the  rock  has  left  these  fossils  stand- 
ing out  in  bold  relief. 

A  fine  section  of  the  stratafied  rock  formation  is 
found  in  Southern  Belle  Canyon.  The  strata  are 
uplifted  and  extend  southward  at  an  angle  of  fif- 
teen degrees.  The  section  consists  of  regular  strata 
of  red  sandstone,  shale,  quartzite,  sandstones  and 
limestones,  resting  upon  diorite.  At  the  eastern 

12 


end  of  the  section,  strata  of  sandstone  and  lime- 
stone abut  upon  granite. 

The  beds  are  the  upper  members  of  the  series 
and  are  probably  Devonian,  as  indicated  by  the 
corals.  The  most  prominent  strata  are  the  massive 
white  quartzite,  with  out-croppings  due  to  fault- 
ing. The  red  shales  of  the  lower  series  pass  into 
red  sandstones  of  compact  and  even  grain.  The  un- 
derlying diorite  penetrates  this  series  of  shales  and 
sandstones  and  is  itself  underlaid  by  coarse  gray 
granite,  which,  near  Oracle,  is  weathered  into  huge 
boulders  by  decomposition. 

There  are  several  localities  of  remarkable  con- 
glomerates in  the  northern  and  central  portions  of 
the  Catalinas.  The  component  pebbles  are  chiefly 
quartzite ;  they  are  all  much  rounded  and  show  the 
violent  action  of  currents  and  waves,  indicative  of 
shallow  seas  and  insular  conditions  in  remote  geo- 
logic times. 

RINCON  RANGE 

The  central  and  higher  portions  of  these  moun- 
tains consist  of  gneissic,  but  toward  Benson,  these 
crystalline  rocks  are  flanked  by  an  extensive  de- 
velopment of  Paleozoic  strata,  chiefly  quartzites, 
shales  and  limestones,  uplifted  and  contorted  and 
underlain  by  coarse  granite.  Silicified  corals  abound 

13 


and  indicate  a  Devonian  horizon  above  the  basal 
quartzites  which  are  probably  Cambian. 

THE  VALLEY  OF  THE  SAN    PEDRO  RIVER 

The  valley  east  of  the  Catalina  Mountains  was 
once  the  bed  of  a  lake-like,  or  estuarine,  sheet  of 
water,  named  Lake  Guibaris.  The  San  Pedro  river, 
anciently  the  Guibaris,  in  dry  seasons,  is  an  insig- 
nificant stream,  draining  a  considerable  area.  It  is 
bordered  by  mountain  ranges,  forming  a  valley  1 0 
to  20  miles  wide,  and  about  150  miles  long.  This 
river  has  cut  its  way  through  extensive  horizontal 
beds  of  unconsolidated  light  red  clays  and  sedi- 
ments of  great  thickness,  often  terraced  by  river 
erosion  and  extending  high  up  the  sides  of  the 
bordering  mountains.  Benson,  in  the  bottom  of  the 
valley,  has  an  altitude  of  3,576  feet.  The  lacus- 
trine clays  rise  from  this  point  on  each  side  to  a 
height  of  3,000  feet.  It  appears  that  the  height  of 
the  water  was  about  4,000  feet  above  the  tide. 
Wells  bored  in  the  valley  pass  through  similar 
sediments  for  500  feet  without  reaching  bed-rock. 
The  extensive  strata  of  deatomite  and  volcano  ash, 
upward  of  100  feet  thick,  are  cut  through  by  the 
San  Pedro  river. 


14 


THE  SANTA  RITA  RANGE 

This  range  is  on  the  east  and  south  side  of  the 
valley  of  Tucson,  and  reaches  an  altitude  of  9,432 
feet  in  old  Baldy.  It  is  characterized  by  a  great 
diversity  of  rock  formation,  granitic,  volcanic,  plu- 
tonic,  and  sedimentary. 

The  northern  portion  consists  of  a  broad  devel- 
opment of  paleozoic  strata.  Southward,  are  red 
shales,  limestones  and  basal  quartzites.  The  quartz- 
ites  are  probably  Cambrian.  The  paleozoic  sand- 
stones and  limestones  resting  on  a  granite  founda- 
tion, give  place  to  rocks  of  volcanic  origin,  chiefly 
in  the  form  of  rhyolitic  tuffs,  consolidated  ashes, 
agglomerates  and  porphyries.  The  formations  of 
volcanic  origin  appear  to  constitute  the  bulk  of  the 
main  south  ridge  and  to  extend  to  the  very  summit 
of  the  highest  peak. 

The  celebrated  large  ring  meteorite,  called  the 
Irwin-Ainsa  meteorite,  now  in  the  National  Mu- 
seum, was  found  at  the  mouth  of  Box  Canyon. 

Still  farther  south,  a  compact  strata  of  blue 
limestone  containing  obscure  brachiopod  fossils,  is 
found  dipping  westerly  at  an  angle  of  45  degrees. 

At  the  base  of  the  Santa  Ritas,  is  one  of  the 
most  remarkable  beds  of  large  rounded  porphyry 
boulders  known.  They  are  of  all  sizes  and  colors, 
and  are  closely  compacted  and  may  be  regarded  as 


15 


evidence  of  stupendous  cataclysmic  action.  West 
of  Salero.  there  are  remarkable  strata  of  snow- 
white  tufaceous  flagstones,  so  thinly  and  regularly 
stratified  that  slabs,  yards  in  area,  and  a  few  inches 
thick,  mav  be  broken  out.  They  show  ripple  marks 
on  their  surface,  and  the  whole  series  give  evidence 
of  deposition  in  shallow  water. 

SANTA  RITA  TUFAS 

The  high  peak  of  the  Santa  Rita,  with  its  enor- 
mous flanking  ridges  of  volcanic  ejectamenta,  is 
certainly  a  monumental  relic  of  a  great  center  or 
region  of  volcanic  activity,  from  which  an  immense 
volume  of  broken  rock,  rhyolities  and  ashes  were 
spread  far  and  wide.  This  underlies  the  ancient  de- 
trital  slope  which  overlies  it. 

The  evidence  is  conclusive  that  the  greater  part 
of  the  vast  mass  of  volcanic  ejectamenta  was  spread 
under  water.  We  have  not  only  the  stratafication 
of  the  beds  of  the  Santa  Rita,  but  also  the  white 
feldspathic  flagstones  are  covered  with  ripple 
marks. 

There  is  no  doubt  that  the  enormous  deposits 
around  the  Santa  Ritas  are  of  great  antiquity, 
probably  pre-Tertiary,  antedating  the  continent 
uplift  at  the  close  of  the  Miocene. 


16 


THE  SIERRITAS  AND  TUCSON  MOUNTAINS 

These  mountains,  forming  the  southern  limit  of 
the  valley,  are  largely  granitic,  with  strata  of  sub- 
carboniferous  limestone  and  shales  partly  meta- 
morphic  and  copper  bearing.  The  Twin  Buttes 
copper  mine  is  found  here,  and  other  mines  at 
Mineral  Hill  and  at  Azurite  Camp,  all  in  associa- 
tion with  porphyritic  dikes  and  garnetiferous  veins, 
the  result  of  replacement  of  the  limestone. 

The  Sierritas  give  place  farther  north  to  the  Tuc- 
son Mountains,  composed  largely  of  volcanic  tufas 
and  agglomerates.  The  tufas  are  regularly  strati- 
fied and  uplifted.  They  are  probably  pre-Tertiary 
or  Cretaceous  in  age,  the  equivalents  in  this  re- 
spect of  the  stratified  tufas  of  the  Santa  Ritas  on 
the  opposite  side  of  the  valley. 

The  western  portion  of  the  Tucson  Mountains 
is  made  up  in  part  of  ancient  sediments  of  paleo- 
zoic age — limestones,  sandstones  and  shales.  Blue 
limestone,  probably  lower  carboniferous,  much 
traversed  by  flint,  crops  out  in  Snyder  Mountain. 
There  are  plutonic  rocks  in  great  variety  in  the 
form  of  dikes. 

The  extensive  rhyolitic  intrusions  north  and 
south  and  on  both  sides  of  the  Santa  Cruz  valley, 
command  attention  as  marking  a  long  line  of  dis- 
ruption and  faulting  of  the  crust,  accompanied,  no 


17 


doubt,  by  crusted  movements  at  different  periods, 
parallel  to  the  axes  of  the  uplift  of  the  paleozoic 
strata.  The  more  distantly  characterized  and  more 
fusible  volcanic  rocks,  less  viscid  than  the  older 
rhyolites  were,  are  of  a  later  age,  and  are  present 
in  the  form  of  basaltic  lavas,  spread  out  originally 
in  great  sheets  in  igneous  outpourings  upon  the 
upturned  edges  of  the  rhyolites  and  other  rocks. 

THE  MOUNTAIN  SLOPES 

The  mountain  ranges  about  Tucson  and  general- 
ly in  the  southwest,  are  separated  by  broad  valleys 
commonly  regarded  as  plains,  or  mesas,  but  in 
reality,  sloping  surfaces  stretching  outward  and 
downward  at  a  gentle  inclination.  The  topography 
changes  rapidly  from  precipitious  declivities  to 
gently  inclined  surfaces  of  gravel  and  loosely  ag- 
gregated material,  the  detrital  accumulations 
washed  out  from  the  ridges  by  streams  and  floods. 
These  deposits  consist  of  boulders  and  fragments  of 
rocks  broken  up  and  partially  rounded,  together 
with  gravel  and  sand,  all  rudely  stratified.  These 
materials  are  coarser  and  heavier  near  the  moun- 
tains than  at  some  distance  away,  where  they  be- 
come more  water  worn  and  fine,  but  large  boulders 
and  coarse  gravels  are  distributed  to  great  dis- 
tances, even  miles  away  from  their  sources,  and 


18 


form  thick  deposits  evidently  of  great  age.  These 
constitute  the  greater  portion  of  the  surface  area, 
estimated  together  with  the  alluvius  at  not  less 
than  nine-tenths  of  the  whole. 

The  angle  of  inclination  is  greater  near  the 
ridges,  but  for  the  middle  and  lower  parts  of  the 
slope  from  80  to  100  feet  per  mile  is  a  common 
gradient. 

These  slopes  are  undoubtedly  of  different  ages 
as  the  higher  ones  are  beyond  the  reach  of  present 
streams  or  floods. 

FORMER  LACUSTRINE  CONDITION 

The  evidences  of  emergence  and  uplift  given  by 
the  detrital  slopes  are  supported  by  the  phenomena 
of  ancient  lakes  or  estuarine  deposits.  The  depos- 
its show  the  long-continued  existence  of  a  large 
body  of  water  with  its  surface  on  or  near  the  four 
thousand  feet  contour  line.  The  uplift  of  the  region 
and  the  advent  of  the  Santa  Cruz,  with  the  cutting 
down  of  its  channel,  brought  these  clay  deposits  to 
view. 

The  fact  of  their  being  such  an  enormous  vol- 
ume of  detrital  materials  filling  the  valleys  and 
composing  the  slopes,  bears  testimony  to  long  per- 
iods of  erosion  and  degradation  of  the  land,  and 
to  eras  of  greater  rainfall  than  we  have  now. 


19 


CHANGE  OF  CLIMATE 

A  change  of  climatic  conditions  throughout  the 
southwest  and  especially  in  the  semi-arid  region  of 
Arizona  and  New  Mexico,  is  marked  everywhere 
by  evidence  of  a  much  heavier  rainfall  than  we 
now  have.  River  valleys  in  many  cases  show  only 
dry  gravelly  or  sandy  beds,  which  evidently  were 
formerly  occupied  by  continuous  streams.  Even 
existing  streams  in  times  of  great  flood  do  not  reach 
their  former  carrying  capacity  or  volume,  and  tell 
of  diminished  volume.  We  may  believe  'hat  the 
era  of  greater  precipitation  in  the  southwest  and 
elsewhere  was  coincident  with  the  widest  extension 
of  glaciers,  and  that  while  the  higher  mountains 
were  being  loaded  with  snow,  the  lower  slopes 
were  deluged  with  rain.  The  gradual  desiccation 
of  Arizona  and  other  regions  may  be  regarded  as 
synchronous  with  the  gradual  disappearance  of 
glaciers. 

EXTINCTION  OF  THE  GREAT  MAMMALS 

The  fact  of  the  existence  and  wide  geographical 
range  in  Arizona  of  the  great  mammals,  the  mam- 
moth and  the  mastodon,  show  a  very  different  con- 
dition of  vegetation  up  to  a  comparatively  recent 
geologic  time.  The  extinction  of  these  great  Herbi- 


20 


vora  may  be  best  explained  upon  the  theory  of  the 
disiccation,  rather  than  by  a  change  in  temperature 
or  increasing  cold.  A  great  change  in  rainfall  and 
the  drying  up  of  the  slopes  and  mesas  of  Arizona, 
must  have  caused  a  great  change  in  the  growth  of 
plants,  involving  their  extinction  over  great  areas. 
It  would  appear  that  the  extinction  of  the  giant 
mammals  and  the  disappearance  of  suitable  vege- 
tation for  their  sustenance  proceeded  together  and 
were  due  to  increasing  heat  and  dryness  rather 
than  to  increasing  cold. 

The  coal  beds  near  Deer  Creek  give  ample  evi- 
dence that  in  the  Cretaceous  era,  conditions  were 
favorable  to  forest  growth  and  luxuriant  vegeta- 
tion in  the  vast  swamps  that  were  widespread  then. 

Quantities  of  silicified  tree  trunks  near  Yuma, 
and  the  giant  stone  trees  of  the  Petrified  Forest, 
bear  testimany  to  such  forest  growth  and  to  the 
destructive  climatic  changes  in  the  Tertiary. 

A  thick  accumulation  of  spragnum  with  stumps 
of  trees,  and,  at  the  bottom,  teeth  of  the  mastodon, 
are  found  in  Davidson's  Canyon. 

The  former  existence  in  Arizona  of  a  species  of 
Bos  of  unusual  size  is  shown  by  the  discovery  of 
enormous  horn-cores  in  the  gravels  of  the  deriva- 
tive slopes  of  the  Santa  Ritas,  at  Greaterville. 


21 


SUBMERGENCE  AND  ELEVATION 

The  comparatively  general  and  uniform  altitude 
of  the  detrital  slopes  favors  the  view  that  the  sea 
level  rested  for  a  long  period  at  about  the  4,000- 
foot  contour. 

The  salient  features  of  the  submergence  then 
are — 

1 .  The  wide  extension  northward  and  eastward 
of  the  Gulf  of  California,  northward  up  the  valley 
of  the  Colorado  River  to  and  into  the  Grand  Can- 
yon and  into  Nevada 5  eastward  to  the  upper  Gila, 
and  Salt  River. 

2.  The  deeply  indented  and  rocky  coast  line  of 
Arizona  with  many  estuaries  and  bold  headlands. 

3.  The  insular  condition  of  the  region  of  Tuc- 
son east  and  west  of  the  valley  of  the  Santa  Cruz, 
of  the  San  Pedro,   and   Sulphur  Springs   Valley 
forming  a  veritable  archepelago,  in  which  the  San- 
ta Catalinas,  the  Rincons,  the  Santa  Ritas  and  the 
Tucson  Mountains  formed  prominent  islands. 

4.  The  southern  coast  ranges  of  California  dis- 
appear under  water,  while  the  southern  end  of  the 
Sierra-Nevadas  appear  as  a  long  narrow  promon- 

22 


tory  disconnected  at  the  Canyada  de  las  Uvas  from 
the  Sierra  Nadrea,  and  at  San  Bernardino  from  the 
San  Jacinto  and  the  Peninsular  Range  of  Moun- 
tains. 

Finis 


2.1 


L.H5KAK1 

UMiYBKSITY  OF  CALIFQBim 
LOS 


IIIIIIIIIIIIIllllll 

A     001  177409     8 


